Java Cookbook, 2nd Edition

Chapter 17. Server-Side Java: Sockets

Introduction

Sockets form the underpinnings of almost all networking protocols. JDBC, RMI, CORBA, EJB, and the non-Java RPC (Remote Procedure Call) and NFS (Network File System) are all implemented by connecting various types of sockets together. Socket connections can be implemented in many languages, not just Java: C, C++, Perl, and Python are also popular, and many others are possible. A client or server written in any one of these languages can communicate with its opposite written in any of the other languages. Therefore, it’s worth taking a quick look at how the ServerSocket behaves, even if you wind up utilizing the higher-level services such as RMI, JDBC, CORBA, or EJB.

The discussion looks first at the ServerSocket itself, then at writing data over a socket in various ways. Finally, we show a complete implementation of a usable network server written in Java: the chat server from the client in the previous chapter.

17.1. Opening a Server for Business

Problem

You need to write a socket-based server.

Solution

Create a ServerSocket for the given port number.

Discussion

The ServerSocket represents the “other end” of a connection, the server that waits patiently for clients to come along and connect to it. You construct a ServerSocket with just the port number.^[1] Since it doesn’t need to connect to another host, it doesn’t need a particular host’s address as the client socket constructor does.

Assuming the ServerSocket constructor doesn’t throw ...